Here's why the Apple iPhone 5s' accelerometer is off

posted by Chris P. / Oct 17, 2013, 2:21 AM

A little over ten days ago, we
reported on what turned out to be a widely publicized issue with the
new Apple iPhone 5s – it's accelerometer. It's
been reported and confirmed
beyond a shadow of doubt
that the sensor is way off, though the exact cause split the
community of unhappy Apple customers in two: some suggested that it's
a software-side thing, while the rest argued it's the hardware.

According
to RealityCap CEO and developer Eagle Jones, its the latter that had
it right all along. As we noted in our previous report,
Apple has gone ahead and switched its partner for the precision
device from STMicroelectronics to Bosch, which would've been a-okay,
but as it turns out, the new part actually appears inferior. Before
you understand why, it's helpful to understand that accelerometers
rely on two key measurements to showcase the level of their
accuracy: bias and variance. The former describes the level of
constant inaccuracy stemming from the hardware process, while the
latter simply rates the consistency of an accelerometer's readings. Jones further explained this in an e-mail to
Gizmodo:

“Let's
say we're just measuring the strength of gravity, which should be
9.81 m/s^2.

All
fine and dandy, but it would appear that while variance for the two
products is almost identical, the bias values differ greatly:

This
is where we find the problem: the typical bias for the ST part is +/-
20mg,
while the Bosch part lists +/-95mg. This
almost 5x greater offset range is confirmed by our measurements, and
is absolutely consistent with the failures being reported by users
and the media.
Specifically, a +/- 20mgoffset
range would translate to around a +/-1 degree accuracy range in tilt
detection, and a +/-95mgoffset
translates to +/-5 degrees in tilt.

Meaning
that iPhone 5s' equilibrium measurements can be off to a pretty wide margin if you're unlucky and get a more extreme case. What's more,
Jones told Gizmodo that Apple could have actually compensated for this
change with further factory calibration, but for whatever reason –
they didn't. Luckily, according to Jones, this can still be salvaged,
though the work-around and this whole issue will definitely serve to
tarnish Apple's image of shipping products that just work from the
onset:

It
is possible to work around the problem by incorporating a calibration
procedure into apps. This procedure would ask the user to place the
device in different orientations to determine the accelerometer bias.
Apps can then subtract this measured bias from the data coming from
the accelerometer to get a corrected reading.

What's
most disappointing, though, is that we still haven't heard of Cupertino on the
issue, which is probably smart on their end. That's not to say that it's not important
– anything from gaming, to use of any tools and apps that take
advantage of your iPhone 5s' accelerometer, down to the touted
dedicated M7 chip can and will be affected.

posted on Oct 17, 2013, 2:32 AM 0

Posts: 78; Member since: Jun 06, 2013

posted on Oct 17, 2013, 5:10 AM 0

actually it wasn't a biased comment to begin with. I was just stating an error that I ran into. but i'm not surprised with your comment as this website is full of one-sided fanboys trying to start flame wars. To clear up any misunderstandings with the profile icon I have put in place, I have appreciation for every smartphones on the market and while I do prefer android at the moment as opposed to other platforms, I still think that ios, windows, bb, and other newer platforms are quite awesome.

posted on Oct 17, 2013, 3:28 AM 2

Posts: 2036; Member since: May 29, 2013

Apple: Your wifing wrong.
Heres another oen about lag on the iphone 5s/browser.
http://www.youtube.com/watch?v=LY-KuPhC0Y0
Either IOS 7 is really unoptimized or apple is faking benchmarks for the A7. If they are faking benchmarks hopefully the jail breaking community exposes them.

Posts: 158; Member since: Jul 06, 2013

posted on Oct 17, 2013, 3:56 AM 1

Posts: 356; Member since: Mar 19, 2013

The FACT is that every measuring instrument has some inherent error and that has to be accounted for via calibration. These days calibration correction factors are mostly done in software. The new part may be inferior from a HW perspective, but it can still be calibrated.

posted on Oct 17, 2013, 8:01 AM 0

Posts: 7305; Member since: Dec 05, 2009

First: you misspelled "accuracy." Not a big deal, and I'm sure you'll fix it, but it tickles my "irony" sensor and made me smile.
Second: Apple is probably figuring out how best to handle this before going public with a response. With all the competition out there they would suffer from another "Antennagate" issue: a relatively minor design flaw/defect that got blown way out of proportion by the ineptitude of Apple's responses. They really, REALLY don't want to mishandle this issue as the holidays are coming up like a freight train, as Apple already has enough trouble figuring out how to sell its 5c stock.

posted on Oct 17, 2013, 3:36 AM 2

Posts: 4062; Member since: Jul 23, 2013

This is what happens when you desperately try to cut costs to increase margin and end up decreasing value. Welcome to the real post-Jobs Apple, where cool stuff takes a back seat to the money in a big way.

Posts: 3718; Member since: Nov 03, 2012

posted on Oct 17, 2013, 4:33 AM 2

Posts: 813; Member since: Jun 10, 2013

If Apple had the procedures for users to calibrate the sensors, the impression of things working perfectly out of the box would be dead. Other than that, I'd like to know the reason they changed supply companies for the sensor. If it was just to get a cheaper priced product over getting a quality product, shame on them.

This copy is for your personal, non-commercial use only. You can order presentation-ready copies for distribution to your colleagues, clients or customers at https://www.parsintl.com/phonearena or use the Reprints & Permissions tool that appears at the bottom of each web page. Visit https://www.parsintl.com/ for samples and additional information.